But there is another signal advantage in the medical point of approach to a relationship which, as I have said, must be friendly in fact, not merely in name, if it is to succeed in any of its ulterior objects. When the social worker begins the difficult task of acquiring her influence in a family, she starts with a great deal in her favor if she appears in the home as _the agent of the physician_. He has prestige. By reason of his profession, by reason of the institution which he represents, by reason of confidence already established by him in the patients' friends and neighbors, the new family is ready to have confidence in him. He is not thought to have any axe to grind. He is assumed to be genuine in his desire of helpfulness. Therefore any one who appears in his name, as his assistant, has a great deal in her favor, especially when compared with the visitors of societies which might be supposed to begin with economic or moral suspicions about the family. If the visitor appears in the home with the prestige of a medical institution enhancing the value of her own personality, she has a very definite advantage. _Light on the severity of illness_ I have said that it is essential to the success of a medical visitor's work that she should be part of the medical machine, acknowledged as the doctor's agent, concerned wholly with helping to carry out his plans. But we must ask now, _what part_? And the answer is that the social worker is an assistant to the physician both _in diagnosis and in treatment_. I will begin with an account of what she is to do as his assistant in diagnosis. She is to discover, so far as she can, _what_ the disease is, _how much_ the disease is, and _why_ it is. I do not mean, of course, that she is to ape the doctor's scientific investigations, that she is to use instruments of precision, or to try to prescribe medicines. But she is to help the physician in some of the following ways: